According to a mining method adopted in a large-scale open-pit (surface) mine or the like, earth is broken up beforehand by blasting, followed by the digging of this broken-up earth with an excavator, for example, a hydraulic shovel. This will be described with reference to FIGS. 19, 20 and 21. FIG. 19 is a plan view of the entirety of a large-scale mine. In this drawing, letter A indicates the whole area of the large-scale mine, which is as wide as several kilometers or longer in both length and width. Designated at signs A.sub.1 -A.sub.n are lots formed by dividing the whole area A into smaller sections. Each lot is set so that it is about 50 to 200 m in both length and width. Letter B indicates a mine management office which performs management of this mine site. The mine management office B is built at a position which is convenient for the management of both the inside and outside of the whole area A.
FIG. 20 is a plan view of one of the lots shown in FIG. 19. In this case, the lot A.sub.1 depicted in FIG. 19 is shown in the form of a square. Signs P.sub.B1,P.sub.B2, . . . , P.sub.Bi, . . . indicate blasting positions in the area A.sub.1. Further, signs d.sub.1,d.sub.2 indicate distances between the respective explosives. In general, these distances are often set substantially equal. The placement positions (distances) and amounts of explosives are determined in view of cylindrical samples, which are obtained by conducting a geological survey at predetermined positions in the whole area A, and a topographical map of the whole area.
FIG. 21 is a side view of a hydraulic shovel. After completion of blasting by explosives placed in a lot, one or more hydraulic shovels enter the lot to dig the blasted earth and then to load it on dump trucks or the like. The blasted earth is transported to a predetermined place and is processed there. The hydraulic shovel illustrated in FIG. 21 performs this digging work. In the drawing, there are shown a travel base 1, a pivot cab 2, a cab 3, a boom 4 pivotally supported on the pivot cab 2, a boom cylinder 4S for driving the boom 4, an arm 5 pivotally supported on the boom 4, an arm cylinder 5S for driving the arm 5, a bucket 6 turnably supported on the arm 5, a bucket cylinder 6S for driving the bucket 6, and a hinge 6p as a center line of turning motion of the bucket. Letters C and D indicate a crowding direction and a dumping direction, respectively, in the operation of the bucket. Digging is performed when the bucket 6 is operated in the crowding direction C, whereas release of dug earth from the bucket is performed when the bucket 6 is operated in the dumping direction D.
Upon completion of the above-described digging work in one of the lots, explosives are next planted in the next lot. These explosives are fired, and the blasted earth is dug by the hydraulic shovels. The dug earth is transported away by dump trucks or the like. Digging work of the individual lots is successively performed in the manner as described above.
The removal of overburden is considered to account for 80% of the above-described work in the large-scale mine. Accordingly, whether blasting is proper or improper has an overwhelming influence on the entire work. Described specifically, use of explosive in unduly small amounts or setting of blasting positions at excessively large distances makes it impossible to break up earth sufficiently loosely. In this case, large digging loads are applied to the hydraulic shovels. More time is therefore spent digging, resulting in the digging not being able to be performed as scheduled. This also leads to an inconvenience in that dump trucks are kept on standby for a long time. On the other hand, use of explosive in excessively large amounts or setting of blasting positions at excessively small distances results in excessively loose breakage of earth. This leads not only to a problem of the digging ability of the hydraulic shovels not being able to be used fully but also to another problem of cost for the explosive being substantial. A blasting planner makes a blasting plan for the next lot by observing the state of earth after the blasting or by learning of the state of digging from the operators of the hydraulic shovels. Both this observation and learning rely upon the sensations of the planner and those of the operators, respectively, thereby making it impossible to perform optimal blasting in many instances.
An object of the present invention is to provide a measuring and display system for loads applied upon digging blasted earth, which can solve the above-described inconveniences and problems of the conventional art and can contribute to accurate blasting.